Standards compatibility improvements include provision for the Netscape plugin API, allowing most Netscape plugins to be used in-process, support for HTML 5 audio and video elements using Qt's Phonon integration, and facilities for client-side storage of Web content.

A new OpenGL ES 2.0-based paint engine complements the existing OpenGL paint engine, but with a focus on embedded devices.

Qt now features a pluggable graphics system, making it possible for users and developers to select raster, OpenGL or native graphics systems to take into account the specific needs of their applications and get the best performance out of them.

For many applications, a simple recompilation is all that is required to produce an executable for 64-bit systems. Applications that use specific features may require a few changes first.

Windows CE Feature Parity

Qt for Windows CE has been updated to bring features of Qt 4.4 and Qt 4.5 to the Windows CE platform, including:

Phonon Multimedia Framework, using a Direct-Show based backend for audio and video playback and a Simple WaveOut backend for devices without DirectShow.

The inclusion of Qt WebKit integration features previously unavailable for Qt 4.4 on Windows CE.

Support on all Windows CE platforms; recommended for WinCE 6 and higher.

The inclusion of these features enables developers to easily integrate Web and multimedia content into Qt applications on Windows CE Standard Edition while retaining full cross-platform compatibility with other Qt platforms.

XML Transformations with XSLT

Модуль QtXmlPatterns был расширен для того, чтобы охватить XSLT, язык преобразований документов XML. A common application of this is the transformation of XML data into human-readable formats for reporting purposes.

XSLT makes it simple to reformat XML content without changing data structures, removes the need for an intermediate DOM layer for presentation, and enables rapid solutions to be created; for example, creating reports as HTML or PDF.

Qt Script Debugger

Developers using Qt Script in their applications can take advantage of the new Qt Script Debugger to provide error reporting for scripts, and to let users track down bugs in their own scripts.

Many standard features of GUI debugging tools are present, allowing the developer to step through running script code, inspect variables, automatically catch exceptions, and set conditional breakpoints.

Improved Network Proxy Support

Qt's networking classes have been updated with improved proxy support. This includes improved integration with system proxy settings and the added ability to handle non-trivial proxy cases.

Qt Designer Improvements

Qt Designer 4.5 boasts some improvements on usability, for example:

Icon Mode for the widget box which substantially reduces scrolling.

Morphing Widgets which lets you morph similar widget types, e.g., a QWidget to a QFrame, types via the context menu's Morph into entry.

Filters for the Property Editor that lets you find properties or widgets quickly.

Find option for the Object Inspector that performs an incremental search on the form's widgets. Also, the objects' layout state is displayed here with using an icon on the left. Broken layouts are represented with the same icon used for the Break Layout action.

In addition, Qt Designer now features an Embedded Design tab that can be found in the Preferences dialog. Within this tab, you can define embedded device profiles. These profiles contains screen settings, e.g., display resolution, default font and default style. Qt Designer will use these settings when you edit forms.

Qt Linguist Improvements

Support for XML Localization Interchange File Format (XLIFF) files, previously added to the lupdate tool in Qt 4.3, has been improved and extended to the rest of the Qt Linguist toolchain. This enables files stored in Qt's TS translation format to be exported for use with other tools.

The GNU Gettext PO format, which is commonly used in Open Source projects, is now supported by Qt Linguist.

Support for a new way to annotate messages, using comments in the source code, has been added to the toolchain. See the QObject::tr() documentation for a detailed description and examples.

The new lconvert filter tool facilitates conversion between file formats and can be used to perform other transformations on collections of translatable strings.

Graphics Enhancements

In addition to the performance improvements in this release, a number of graphics enhancements extend support for existing features to more platforms and expand Qt's core set of features with successful add-ons.

Widget style sheets can now be used on Mac OS X, making this approach to theming and styling viable for truly cross-platform applications.

Support for ARGB top-level widgets, previously available as a separate solution, is now provided as an integral part of Qt. This makes it possible to create windows with translucent regions on systems with the appropriate support from the user's window system. See the Creating Translucent Windows section of the QWidget documentation for details of this feature.

Improved GTK+ integration provided by the QGtkStyle class improves the look and feel of Qt applications in GNOME and other GTK-based environments. The screenshot above illustrates this clearly.